The long term objective of this proposal is to understand the neuronal organization that underlies the generation of behaviors by simple nervous systems. To accomplish this goal, we will use voltage sensitive dyes imaging techniques to monitor a large fraction of neurons when behaviors are generated. We plan to study two molluscan ganglia, the Aplysia abdominal ganglion and the Clione intestinal ganglion. We have found that about 300 neurons are activated in the Aplysia abdominal ganglion during two kinds of gill withdrawal behaviors and about 70 per cent of the active neurons are activated in both behaviors. This suggests there may be a large distributed neuronal network in this ganglion. For Aplysia, we plan to monitor a large fraction of neurons during normal and altered behaviors. There are four specific aims: I. To test three models for possible neuronal organization suggested by our preliminary data. II. To examine how neurons are shared by different behavioral events III. To examine the interaction between evoked behavior and intrinsic rhythms and between two behaviors initiated close in time. IV. To study how system changes when the activity of individual neurons is modified and to find important interneurons in the ganglion. With these aims we will try to understand the neuronal organization in this ganglion and the role of individual neurons in a large and extensively inter- connected neuronal network. We will also examine the dynamic behavior of this simpler nervous system and explore the hypothetical "temporary circuits" which forms only during specific behaviors. We also plan to study a smaller nervous system-- the Clione intestinal ganglion. This ganglion has been evaluated in our preliminary experiment and may be unique for optically monitoring all the neurons during behaviors. Two specific aims are proposed on this new preparation: I. To identify all the neurons in the ganglion by combining voltage sensitive dye imaging and phase contrast enhancement. Neurons will be identified by both morphological features and the activity patterns during different behaviors. II. To study how neuronal activity changes when the neuronal hardware varies. We have found that there are a large variations in number of neurons in this ganglion. We will try to examine how neuronal activity patterns change when neurons are missing or there are extra neurons.